In the melt-spinning of filaments from synthetic organic polymers, the polymer is extruded downwardly with the aid of a spinning pump or some other device through a plurality of orifices in a spinneret (or spinnerette) to form molten filaments. The extruded molten filaments are attenuated while passing through a quench zone where a stream of fluid, such as air, is passed across the path of the filaments to cool or solidify them. By application of a draw force the filaments are attenuated into finer filaments until their surface solidifies. When solidified the filaments can be deposited onto a collection surface to form a web. Beams used for melt-spinning polymeric filaments are typically provided with spinnerets that comprise capillaries that are uniformly spaced and have similar exit diameters as well as similar lengths throughout the entire array of capillaries in the spinneret. Several previous variations of these uniform designs of capillary layouts and capillary dimensions in spinnerets are discussed hereinbelow.
In U.S. Pat. No. 4,248,581 (“581 patent”), a process for determining the arrangement of orifices in a spinneret is disclosed. The '581 patent does not appear to disclose variations in any orifice dimensions other than the spacing between orifices.
In U.S. Pat. No. 4,514,350 (“350 patent”), spinnerets are shown which have “graduated orifice sizes” (GOS) that are used in manufacturing melt-spun filaments with good birefringence (i.e., molecular orientation) uniformity at high polymer extrusion rates. The '350 patent does not relate to providing changes in length to hydraulic diameter ratio in different groups of different shaped capillaries in the spinneret, nor changes in length to hydraulic diameter ratio for any two or more different adjacent groups of capillaries in the spinneret, nor indicate that these parameters may effect spinneret, filament, and fabric performance.
In U.S. Pat. No. 5,266,255 (“255 patent”), a process is shown for high stress spinning of polyethylene terephthalate yarns to produce a yarn of high birefringence by using a spinneret having at least one row of orifices with a diameter greater than an adjacent row of orifices. The '255 patent does not appear to disclose variations in any other orifice dimension than diameter.
In U.S. Pat. No. 5,112,550 (“550 patent”), a process and apparatus for producing superfine fibers is shown that uses a spinneret having nozzle orifices arranged in a lattice pattern extending toward a quench direction and the right angled direction to the quench direction with the arrangement being provided to satisfy certain formulae described therein. However, the '550 patent does not appear to disclose orifices (e.g., capillaries) that have different diameters or lengths, or different ratios thereof.
The present inventors have recognized that there is a need for a spinneret with a plurality of zones having various combinations of capillaries with various dimensions that can accommodate higher overall polymer throughputs and produce uniform filaments while minimizing filament breaks and nonwoven web and fabric hard spot defects.